Để nhanh chóng xác định các lớp học để có một địa chỉ IP thuộc, bạn có thể thực hiện theo một quy tắc dễ dàng. Nó được biết đến như nguyên tắc octet đầu tiên và được minh họa trong Bảng nhanh và dễ dàng Rule của octet thứ nhấtHơn nữa | TCP IP and the OSI Model Chapter 3 93 To quickly identify the class to which an IP address belongs you can follow an easy rule. It is known as the first octet rule and is illustrated in Table . Table Quick and Easy Rule of the First Octet Class First Octet Rule Decimal Binary A First bit 0 0-127 00000000-01111111 B First two bits 10 128-191 10000000-10111111 C First three bits 110 192-223 11000000-11011111 D First four bits 1110 224-239 11100000-11101111 E First four bits 1111 240-255 11110000-11111111 Furthermore within each class is an address range reserved for private private addresses are as follows and . In many cases these addresses are designated for devices that will not be sending or receiving traffic outside their own networks. Another possible application for private addresses is a situation in which only a limited number of people would be communicating outside their network at any one time. In this case an address pool would be established in which addresses are dynamically assigned to a device for a limited is a measure to help conserve address space. These few private address ranges along with a few others are the only addresses that are not permitted on the Internet. For a complete list of all the Internet addresses go to in-notes iana assignments ipv4-address-space. Conserving Address Space with VLSM It was identified early in the development of the Internet that the limited number of IP addresses would eventually run out so a method of splitting classes into smaller blocks needed to be developed. Conservation efforts are absolutely necessary. Let s think about why this is important. Imagine that you are the owner of a large telecommunications 94 Chapter 3 TCP IP and the OSI Model support voice and data which means that you might have a Frame Relay network an ATM network an IP network and so on. Not .
